Stop punishing yourself for mistakes.
Every person at least once in his life has made wrong decisions, said unnecessary things, missed opportunities or done something that he later regretted. But mistakes are not proof of your incompetence and are not a reason to deny yourself peace of mind forever. They are part of the human experience through which we get to know ourselves better, our weaknesses, the true values and the consequences of our actions.
It is important not only to regret what happened, but to try to understand what this experience taught you. If you have hurt someone, find the courage to admit it, and if possible, correct what you have done. If you made a wrong decision, learn a lesson. But don't make the past a place where you judge yourself over and over again for things you can't change. Remember that the person you were then did not have the understanding and life experience you have today. Don't demand from your past the wisdom you acquired only during the years you lived.
Accept your mistakes, learn from them and leave your regrets behind. You don't have to pay for the rest of your life for not knowing or understanding something once. You still have a chance to do things differently.